A Guide to Cleaning Composite Decks

Most consumers who opted for composite lumber for their decks did so with the idea that it would be maintenance-free and free from the kind of aging problems (warping, cracking, splitting, etc) that are often seen with pressure-treated lumber. Hindsight is always 20-20, as the old saying goes. Most of these customers are realizing that no wood or wood product exposed to weather is going to be completely maintenance-free. Even exotic woods like Ipé require periodic cleaning and sealing as the natural oils within the wood dry out.

Composite lumber varies from manufacturer to manufacturer, but it appears that all of the popular ones contain wood particles (these ground particles are called “wood flour” by the industry). That means that any of these particles on or near the surface of the board, no matter what they are mixed with, will react to Mother Nature the same way all wood does. Graying and staining are common problems – and the stuff of nightmares for deck owners. Manufacturers are getting calls every day from end users about these issues, and deck restoration contractors are stepping in with the fix.

Cleaning composite decks is important to keep the material looking its best. Properly cleaning composite decks should be done with a composite wood cleaner that is designed specifically for these unique materials. Most pressure washing contractors who do deck renewal are finding success through products made especially for this problem, such as EZ Off Composite Wood Cleaner. The key to this particular product is in the surfactants and cleaning chemicals in its formula.

This guide will give you the basic steps that should be used to get the best results when cleaning composite deck materials.

Preparing the composite deck:

Sweep debris like leaves, twigs and dirt off the deck first. Then rinse off the composite lumber to cool it off and remove heavy built up deposits of dirt and mud. Rinsing off the composite deck first will cool the surface and prevent the possibility of flash drying the composite cleaner when it's applied. Also wet down plants and grass around the deck and if necessary, Cover plants, grass, concrete and any other areas you don't want the composite cleaner getting on.

Use commercial degreasers containing sodium hydroxide and various detergents for removing grease and oil stains.

Spot removers or mineral spirits may be used carefully on stubborn grease or oil stains but should be washed off quickly with water, as it can damage the grain pattern. Spot removers normally include petroleum distillates, xylene, methanol, acetone, or other organic solvents. Use caution if the composite lumber has embedded color, as some solvents may affect the appearance. As always, test your cleaner on an inconspicuous spot.

To remove mold, mildew, and months of accumulated dirt, wash the deck periodically with EZ Off.

The cleaning process:

Apply EZ Off on the railings and floor in manageable sections. Cleaning too large of an area at a time may allow it to dry on the surface which can cause discoloration in some materials. Once the composite cleaner has sat on the surface according to the directions, carefully power wash the surface in the direction of the grain, using less than 800 PSI. Use the pressure washer to “rinse” the surface. Avoid holding the nozzle too close to the composite surface or holding it in any one spot too long. Hold the pressure wand about 8” away from the surface and “sweep” it off in a rinsing motion. Use a “golf swing” motion, and avoid washing each square inch of the surface. Keep the wand moving smoothly over the surface to avoid leaving marks. Proper technique determines the results, so take some time to practice when you are able to. Once you have completed that section, treat the next area and continue until the job is completed.

For regular maintenance, rinse off your composite deck periodically with a hose. Even if your deck appears clean, it is important to prevent build-up of pollen and other debris. Mildew stains may occur where moisture, pollens, and/or dirt are present. Mildew needs a food source to grow, which can be grass, pollens, dirt, debris, wood and wood resins.

To repair scratches, nicks, cuts and grooves in some (un-colored) composite decking materials you can try using a wire brush. Brushing will need to be consistent with the grain of the composite material and the brushed area will weather back in approximately 8-10 weeks. Make sure you try this in a hidden area first! Some materials could become discolored or damaged from wire brushing!

High-pressure washing of composite decks is not necessary or advisable. Instead, use the proper-strength composite lumber cleaners like EZ Off to do all the work for you. Then you simply RINSE using your pressure-washer. Doing it the right way means using your pressure washer to agitate slightly with MODERATE pressure and HIGH water volume. Use the pressure washer responsibly. Too much pressure on the surface of composite lumber can cause damage.